1. Field of the Invention
The present invention relates to a pellicle. Particularly it relates to a pellicle to be used for the production of semiconductor devices such as LSI, ultra LSI, etc., or liquid crystal display devices, which is particularly suitable for photolithography employing a light having a wavelength of at most 220 nm (especially a wavelength of at most 180 nm).
2. Discussion of Background
In recent years, along with high integration of semiconductor devices, there has been a progress in shortening the wavelength of an exposure light to be used for photolithography in the production process. Namely, to draw an integrated circuit pattern on a wafer, a technique is required whereby a fine circuit pattern can be drawn with a narrower line width. To satisfy such a requirement, a light with a shorter wavelength than the conventional g-line (wavelength: 436 nm) or i-line (wavelength: 365 nm), such as a KrF excimer laser (wavelength: 248 nm), an ArF excimer laser (wavelength: 193 nm) or a F2 laser (wavelength: 157 nm), is now being used as an exposure light for a stepper for photolithography.
In photolithography, a method of mounting a pellicle on one side or on each side of a photomask, as a dust proof for the surface of the photomask, is adopted. If scratches or foreign matters are present on the photomask to be used for the exposure, such scratches or foreign matters will be printed on a wafer together with a pattern, thus causing a short circuit or breaking of the circuit, etc.
Here, the pellicle is meant for one formed into a container shape by bonding a pellicle sheet to a pellicle frame to cover a top opening of the frame. The pellicle comprises a flat pellicle sheet (in this specification, it includes both a membrane-shaped one made of an organic resin and a sheet-shaped one made of e.g. synthetic quartz glass), and a pellicle frame having a predetermined thickness to have the pellicle sheet distanced from the photomask and is one formed into a container shape by bonding a pellicle sheet to the upper face of the pellicle frame. For the pellicle frame, an aluminum having alumite treatment applied to the surface, is employed.
Further, usually, vent holes are formed on the pellicle frame, so that air permeability is secured in a state where the pellicle is mounted on a photomask, thereby to minimize the influence over the pellicle sheet of the changes in the temperature or in the pressure of the external atmosphere.
Further, with a pellicle for a F2 laser, it is necessary to replace the internal atmosphere of the pellicle with an inert gas atmosphere. The conventional photolithographic process has been carried out in the atmosphere. However, in a case where a F2 laser is used for exposure, it is necessary to carry out the exposure in an inert gas atmosphere, since oxygen molecules in the atmosphere have absorption at the exposure wavelength of 157 nm.
JP-A-2001-133961 discloses a method for positively replacing the internal atmosphere of the pellicle. Here, an inert gas is introduced into the interior of the pellicle by connecting an inert gas steel bottle to a hole.
However, the conventional vent hole size is not sufficiently large for replacement of the internal atmosphere simply by blowing an inert gas. Conventional vent holes were used to adjust the pressure, and the size was small as compared with the height of the pellicle frame. For example, the size of vent holes was about 0.5 mm, while the height of the pellicle frame made of aluminum was about 5 mm.
On the other hand, when a pellicle is mounted on a photomask, it is important that the entire bottom face of the pellicle frame is bonded to the photomask in close contact without any clearance and sealed not to have a clearance for permitting dust, etc, formed. For such sealing, a pressure sensitive adhesive may be coated on the end face of the pellicle frame on the photomask side, or the pellicle frame is mounted on the photomask by means of a pressure sensitive adhesive tape. At that time, by means of a pellicle mounter, a load of at least 30 kg may be exerted to the upper portion of the pellicle to increase the sealing degree.
By a study by the present inventors, it has been found that the exposure pattern may have a distortion if vent holes are enlarged in order to let the pellicle atmosphere be replaced passively. Namely, the frame may have a distortion by the load at the time of mounting the pellicle to the photomask. Further, at the time of drilling the pellicle frame to form vent holes, a residual stress is likely to remain in the pellicle frame, whereby the flatness of the upper and bottom faces of the pellicle frame may deteriorate. If a photomask after mounting the pellicle, has a distortion for such a reason, the exposed pattern tends to be a double exposure, or the exposure position is likely to shift, thus causing a failure. Especially, the pressure required to mount a pellicle on a photomask, increases as the photomask is large-sized, and the possibility of a failure due to such distortion is increasing.
It is an object of the present invention to facilitate replacement of the atmosphere in the pellicle by simple blowing of an inert gas and to obtain a pellicle which will not have a distortion of the exposure pattern. Namely, it is an object of the present invention to reduce the deterioration in strength of the pellicle and to provide a pellicle having the inert gas replacement speed improved, by optimizing the structure of the above-mentioned vent holes.
The present invention has been made to solve the above-mentioned problems, and it provides a pellicle comprising a box-shaped pellicle frame having top and bottom openings, and a pellicle sheet bonded to the pellicle frame to cover one of the openings of the pellicle frame, wherein the pellicle frame is made of quartz glass, a plurality of vent holes are formed as distributed on opposing side walls of the pellicle frame, and the size of the vent holes in the direction of the height of the pellicle frame is at most ⅗ of the height of the pellicle frame.
According to the present invention, the pellicle frame is made of quartz glass, a plurality of vent holes are distributed on opposing side walls of the pellicle frame, and the size of the vent holes in the direction of the height of the pellicle frame is at most ⅗ of the height of the pellicle frame, whereby it is possible to reduce the distortion of the pellicle due to the load at the time of mounting and to reduce a deformation of the pellicle frame due to the residual stress formed by the processing to form the vent holes. Further, replacement of the atmosphere in the pellicle by simple blowing of an inert gas, can be facilitated.